The present invention relates to the field of horology. It concerns, more specifically, power reserve indicator mechanisms for a timepiece movement of the type fitted with an energy source formed of a mainspring. In a conventional manner, the mechanism according to the invention includes a frame, a power reserve indicator and a differential gear with a first input coupled to a wheel set driven in rotation when the mainspring is being wound and a second input coupled to a wheel set driven in rotation when the mainspring is let down, and an output coupled to the power reserve indicator. In such a mechanism, the indicator is able to cover a given angle comprised between two end positions, the first of which is occupied when the mainspring is wound and the second, when the spring is let down.